An example of a tire retreading process which utilizes both inner and outer curing envelopes to completely encase a tire is disclosed in the present assignee's U.S. Pat. No. 5,007,978 issued to Presti. Worn tread on a used tire casing is buffed off to a profile suitable for mounting a new tread. A pre-cured and buffed tread is adhered about the periphery of the casing with a lamina of uncured cushion gum cemented between the tread and the casing. The tire is encased within separate outer and inner curing envelopes and a vacuum is drawn between the envelopes and the tire for stretching the envelopes into intimate contact with all surfaces of the tread and casing. The tire is then placed in an autoclave for several hours at an elevated temperature and pressure to cure the gum and positively bond the casing and tread. The curing envelopes are removed and the retreaded tire is ready for use.
An important step in the above-described tire retreading process is the formation of a vacuum between the curing envelopes and the tire. The vacuum ensures that air or steam does not penetrate into the cushion gum during curing of the gum because the presence of air bubbles, or pockets of air, between the curing envelopes and the tire will prevent proper curing of the gum and will cause tread distortion. In addition, air pockets prevent pressure from being uniformly applied over the entire bonding area which also causes tread distortion.
To eliminate the formation of air pockets between the outer curing envelope and the tire casing and tread, and to ensure the complete evacuation of air from between the outer curing envelope and the tire, the present assignee has long suggested to its customers the placement of a separate wicking material between the outer curing envelope and the tire. Conventionally, the recommended wicking material was a strip of multiple ply nylon. More recently, the recommended wick is that disclosed in the present assignee's U.S. patent application No. 09/046,357, filed on Mar. 23, 1998.
Other tire retreading procedures having enhanced wicking capabilities are disclosed in U.S. Pat. No. 5,173,353 issued to Yamamoto and U.S. Pat. No. 5,306,130 issued to King et al. Neither patent discloses the use of an inner curing envelope; rather, both disclose retreading methods which utilize an outer curing envelope only. The Yamamoto patent discloses placing a separate strip of nylon cloth between the outer curing envelope and the tire for venting purposes. See column 1, lines 14-16 and 27-30 of Yamamoto. The King patent discloses integrally providing a plurality of air passageways on the entire tire confronting face of its outer curing envelope.
Although various ones of the above-referenced retreading wicks or means to vent air between an outer curing envelope and a tire may be satisfactory for their intended purposes, there is a need for an improved means of venting air/gas between an inner curing envelope and the interior surface of a tire casing. Typically, a separate wicking belt is too difficult to properly position between the interior surface of the tire casing and the inner curing envelope. This is especially true if multiple, spaced-apart wicking belts are required to be located between the inner curing envelope and the tire casing. Thus, the wicking means should be capable of ready positioning between the inner curing envelope and the interior surface of the tire casing and should prevent the formation of air pockets when a vacuum is drawn.